Last week the Supreme Court heard opening arguments from the defense lawyers for Proposition 8 and the Defense of Marriage Act, who are apparently both making the same argument: that the government may discriminate against gay people by refusing them marriage rights because they are not capable of having babies by accident:

Conservative attorneys did not argue that gays or lesbians engaged in “immoral” behavior or lifestyles. Instead they emphasized what they called the “very real threat” to society posed by opposite-sex couples when they are not bound by the strictures of marriage.

The traditional marriage laws “reflect a unique social difficulty with opposite-sex couples that is not present with same-sex couples — namely, the undeniable and distinct tendency of opposite-sex relationships to produce unplanned and unintended pregnancies,” wrote Clement, a solicitor general under President George W. Bush. “Unintended children produced by opposite-sex relationships and raised out-of-wedlock would pose a burden on society.”

I had to read this a couple times before I understood the nature of the argument, which is (I think) that unintended births cost the state more money when out of wedlock than in, so the government is justified in offering the financial incentive of legal marriage exclusively to straight couples, who are the only people able to get pregnant unintentionally.

Saying that gay people are, by their nature, more responsible with their family planning seems like a backwards reason to keep them from getting married, but at least this argument has the merit of not being based on something like religious belief or fuzzy evolutionary concerns. Still, I’d like to see some numbers that actually show how the state benefits financially from incentivizing straight marriage.

Even then, I wouldn’t care, though. The long-term social cost of depriving an entire group of marriage rights disturbs me more than the threat of a little additional government expenditure.